The present invention relates generally to optical apparatus and, more particularly, to a nuller.
Extrasolar planets must be imaged directly if their nature is to be better understood. This will be difficult, however, since the bright light from the parent star (or rather its diffracted halo in the imaging apparatus) can easily overwhelm nearby faint sources. Nulling interferometry has been considered a promising technique for reducing a star's brightness relative to its surroundings, which has the potential to enable the direct detection of extrasolar planets and zodiacal light. The technique is based on the precise cancellation, or nulling, of the starlight received by two separate telescopes, and so the amplitudes, phases, and polarizations of the two on-axis electric fields must all be matched to high accuracy across the wave band of interest. To cancel on-axis starlight to high accuracy, some have sought to combine the electric fields from two telescopes viewing a common star exactly out of phase at all wavelengths across the band of interest. One method for introducing the needed achromatic π-rad phase difference is a geometric flip of the electric-field vector, such as that provided by a rotational shearing interferometer. This requires nanometer-level path-length control which is rather complex to implement.